I wouldn't do it. That water is pretty dirty. Plus the sand might have all sorts of debris and other crap in it. Not worth it in my opinion. The cleanest and best sand i've used is the tropic eden sand though.
+1. Unless you're collecting sand from the open ocean, it's likely to have all sorts of contaminants washed in from the waves and isn't worth the headache IMHO. You also run the risk of introducing pests, but that would be the least of my concerns.